COLOR LIQUID CRYSTAL DISPLAY

Abstract: The disclosure is directed to a color liquid crystal display (LCD) using a diffuse light source (10), input and output microlens matrices (16, 24), a color filter layer (14) and an LCD matrix (18) sandwiched between two solid transparent layers (20, 22). The color filter layer is deposited directly upon one of the microlens plates and not upon the glass substrate of the LCD. Thus, a wider variety of substances, primarily dyes, can be used. A wide viewing angle is obtained for a user by virtue of the microlens output. Too, the microlens input plate allows more light from the source to be used.

Description: COLOR LIQUID CRYSTAL DISPLAY BACKGROUND OF THE INVENTION Field of the Invention The invention relates to color displays and, more particularly, to color liquid crystal displays (LCDs) utilizing optically coupled microlens matrices, thereby collecting a greater percentage of the available light to illuminate the matrix of liquid crystal elements and matrix of color filter elements. The invention also isolates the LCD medium from the color filter so that the substances used in the color filter, such as the dyes, need not be inert to the liquid crystal medium. Discussion of the Prior Art Prior art LCD systems typically have color filter dyes deposited directly onto the glass substrate of the LCD. This requires that the substances used in the color filter, primarily the dyes, be inert to the liquid crystal medium. Furthermore, in order to achieve optimum wide viewing angles for users, the spacing of each liquid crystal cell or element, i.e., the cell gap, must be adjusted to an optimum value for the color of the particular cell. SUMMARY OF THE INVENTION In accordance with the invention there is provided a color LCD comprising a matrix of liquid crystal elements positioned within a liquid crystal medium layer disposed between sandwiching transparent layers of material inert to the liquid crystal medium. The color LCD further comprises a uniform light source, a matrix of color filter elements corresponding to the matrix of liquid crystal elements, and first and second matrices of microlens elements corresponding to the matrix of liquid crystal elements and to the matrix of color filter elements. One of the matrices of microlens elements is disposed on each side of the matrix of liquid crystal elements. Corresponding elements of the liquid crystal matrix, the color filter matrix and the first and second microlens matrices are optically coupled to one another and to the uniform light source to provide a viewable color display. The uniform light source preferably comprises a diffuse uniform light source. At least some of the individual lens elements of the microlens matrices are preferably shaped to reduce chromatic aberration for the color of the light to be transmitted therethrough. The color filter elements can comprise additive color dye dots or subtractive color dye dots. Further, the lens elements of at least one of the microlens matrices are preferably larger in cross-sectional area than are the liquid crystal elements in order to utilize a greater portion of the available light than could be utilized without the use of microlenses. The color filter elements are also preferably larger in cross-sectional area than are the liquid crystal elements. The color filter elements can comprise one or more dyes which are reactive with the liquid crystal medium. The color filter layer can be positioned between the light source and the liquid crystal matrix, such as between the light source and the first microlens matrix, or between the first microlens matrix and one of the transparent layers sandwiching the LCD matrix. The color filter layer can alternatively be positioned to color filter the light after it has passed through the liquid crystal matrix. OBJECTS AND ADVANTAGES OF THE PRESENT INVENTION One object of the present invention is to utilize a higher percentage of available light in producing a color LCD. Another object of the instant invention is to minimize chromatic aberrations in a color LCD. One advantage of the present invention is that relatively high intensity is maintained over wide viewing angles on the color LCD of the invention. Another advantage of the invention is that color filters comprising substances which are reactive with LCD media can be utilized. Yet another advantage of the invention is that a lower cost color LCD is producible in accordance therewith. Still another advantage of the invention is that monochrome LCD glass can be used in providing a color LCD. Other objects, features and advantages of the invention will become apparent to those skilled in the art from the description of the preferred embodiment, claims and drawings hereof, wherein like numerals refer to like elements. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically illustrates a preferred embodiment of the invention with the matrix of color filter elements positioned between the input microlens matrix and the LCD matrix; Fig. 2 schematically shows an embodiment of the present invention having the matrix of color filter elements disposed between the LCD matrix and the output microlens matrix; Fig. 3 schematically depicts a third embodiment wherein the matrix of color filter elements is placed between the diffuse light source and the input microlens plate; and Fig. 4 schematically illustrates light paths for corresponding microlens matrix elements and LCD matrix elements. DESCRIPTION OF THE PREFERRED EMBODIMENT As can be seen in Fig. 1, a light source 10 provides uniform and preferably diffuse light through a diffuser 12 and through a color filter layer 14 which may comprise typical additive colors, subtractive colors or additive colors comprising paired layers of subtractive colors, such as disclosed in U.S. application Ser. No. 08/081,915 filed June 22, 1993 entitled "Color Filter Display." Various choices for the color filter dots or elements are well-known and they are disposed in a matrix in a well-known manner. Each color dot is optically coupled with a corresponding individual microlens in a first or input matrix of microlenses on layer 16. Optically coupled to the color dot and microlens matrices is layer 18 comprising a matrix of liquid crystal elements or cells sandwiched between two solid transparent layers 20 and 22. A second or output microlens matrix 24 is optically coupled to the color filter matrix 14, the first microlens matrix 16, and the LCD element matrix 18. In the preferred embodiment, each microlens is preferably corrected for chromatic aberration in accordance with the color of the dot through which it will transmit light. Thus, the individual color elements of filter layer 14 are disposed to be in registry with corresponding individual microlenses in layers 16 and 24 and individual LCD elements or cells in layer 18, so that good alignment of the color filters and lenses is achieved and any chromatic aberration corrected. For example, for a particular green filter dot, corresponding individual microlenses in layer 16 and in layer 24 are corrected to minimize chromatic aberration of green light. Chromatic aberration correction is analogous for the red and blue filtered light. The dots of the filter can be surrounded by black bands as known in the art, if desired. Fig. 2 schematically illustrates an alternative embodiment of the invention wherein the color filter layer 14 is disposed between layer 18 of liquid crystal elements and the second or output microlens matrix 24. Fig. 3 schematically shows another embodiment of the invention wherein the color filter layer 14 is positioned between the light diffuser 12 and first or input microlens matrix 16. All three embodiments illustrated utilize essentially the same combination of optical components. Those skilled in the art will appreciate that a particular embodiment may be the most desirable for a particular application or that manufacturing of one embodiment may be easier or less costly than another. Microlens optical characteristics can be adjusted to compensate for color filter placement, if necessary. Fig. 4 schematically depicts the light paths for corresponding microlens and LCD matrix elements in accordance with the invention. Although not shown in Fig. 4 for the sake of clarity, the color filter matrix 14 is positionable in several places, within the light path of Fig. 4 as illustrated in Figs. 1, 2 and 3. In contrast, typical prior art designs require deposition of the color filter layer directly onto the common electrode surface of the LCD. This layer must then be optically aligned with the active matrix of the LCD and held in precise alignment during subsequent sealing operations. This is usually difficult for a normally black display glass. Misalignment of these layers results in a loss of color purity in the subsequent display and hence the loss of the entire, relatively expensive, active matrix glass. Since, in practicing the present invention, the color filter layer is not deposited on the LCD substrate, a wider variety of materials or substances and processes can be considered for using in constructing the color filter layer. Appropriate choices can save money, decrease manufacturing steps, increase assembly accuracy, and add to the durability of the product. Too, particular dyes which would not be available because they would react with the LCD medium and which are very resistant to fading can be used. Therefore, a much broader universe of dyes can be used to create the color layer. Such dyes may be more stable toward heat as well as light over a normal range of environments to be encountered by the display. Another advantage of the invention is that the use of a matrix of color filter dots deposited onto a microlens plate eliminates a need for a complicated gap adjustment. In the conventional LCD, the cell gap spacing is adjusted for each color in order to - optimize the contrast and viewing angle characteristics of the display. This cell gap adjustment is done typically by depositing additional clear layers of various thickness over or under the color filter layer. Although cell gap adjustment is necessary in the preferred embodiment, yields are increased as a result of separating the cell gap adjustment from the color filter fabrication. Furthermore, in accordance with the invention, since light travels through the LCD with near perpendicular alignment, a wide viewing angle is provided through various designs available for the output microlens plate 24. In addition, in practicing the invention, a monochrome LCD glass, lower in cost than a color panel, can be utilized simply by changing the lens and filter layers which are used with the glass, thereby reducing the number and variety of components that must be inventoried. In this way by practicing the invention, a single LCD glass can be used for monochrome, diagonal stripe color, vertical stripe color, or quad color dot arrangements depending on the lens filter plate to which it is mated. As either additive or subtractive color filter materials can be utilized the advantages of each can be applied to any specific application. Thus, the color filter dots can be produced by, for example, a color printing process in which a printing press or silk screen process is used to deposit a matrix of color dots onto a plate in registry with the microlens matrix thereon. Alternatively, the color patterns can be created using a photolithographic process using patterned polymer layers which are either pre- or post- dyed. The patterns can also be created using color photographic processes such as are utilized to manufacture color transparencies. This invention has been described herein in considerable detail in order to comply with the Patent Statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment details and operating procedures, can be accomplished without departing from the scope of the invention itself.

Claims: CLAIMS The embodiments of the invention in which an exclusive property or right is claimed are defined as follows: 1. A color liquid crystal display comprising: a matrix of liquid crystal elements positioned within a liquid crystal medium layer, said medium layer being disposed between sandwiching transparent layers of material inert to the liquid crystal medium; a uniform light source; a matrix of color filter elements corresponding to said matrix of liquid crystal elements; and first and second matrices of microlens elements corresponding to said matrix of liquid crystal elements and to said matrix of color filter elements, one of said matrices of microlens elements being disposed on each side of said matrix of liquid crystal elements; corresponding elements of said liquid crystal matrix, said color filter matrix and said first and second microlens matrices being optically coupled to one another and to said uniform light source to provide a viewable color display. 2. The invention of claim 1 wherein said uniform light source comprises a diffuse uniform light source. 3. The invention of claim 1 wherein at least some of the individual lens elements of said microlens matrices are shaped to reduce chromatic aberration for the color of the light to be transmitted therethrough. 4. The invention of claim 1 wherein at least one of said color filter elements comprises an additive color dye dot. 5. The invention of claim 1 wherein at least one of said color filter elements comprises a subtractive color dye dot. 6. The invention of claim 1 wherein said lens elements of at least one of said microlens matrices are larger in cross-sectional area than said liquid crystal elements in order to utilize a greater portion of the available light than could be utilized without the microlens. 7. The invention of claim 1 wherein said color filter elements are larger in cross-sectional area than said liquid crystal elements. 8. The invention of claim 1 wherein at least one of the color filter elements comprises a dye which is reactive with the liquid crystal medium. 9. The invention of claim 1 wherein said color filter layer is positioned between said first matrix of microlens elements and said matrix of liquid crystal elements. 10. The invention of claim 1 wherein said color filter layer is positioned between the light source and said first microlens matrix. 11. The invention of claim 1 wherein said color filter layer is positioned to color filter the light after light from the source has passed through said liquid crystal matrix. 12. The invention of claim 1 wherein said color filter layer is positioned to color filter the light before light from the source passes through said liquid crystal matrix.

Inventors: ROBINDER RONALD C, ROBINDER, RONALD, C.
Applicants: HONEYWELL INC, HONEYWELL INC.
Application year: 1994
Main classification: G02F1
IPC codes: G02F1